About the Solar Cooling special technical group

AIRAH’s special technical groups (STGs) provide a way of channelling specialist expertise from the wider industry into the Institute. They give their constituents – who are all AIRAH members as well as elite practitioners – a platform for involvement in issues that affect their discipline, including policy advice and regulation development. The Solar Cooling STG is made up of individuals who are interested in developing the Solar Cooling industry in Australia, with the aim of combating climate change by reducing greenhouse gas emissions (GHG) from the residential and commercial building sectors.

The group is open to all AIRAH members interested in contributing to the future of the Australian Solar Cooling industry. An information stream also exists for others interested in the development of the industry and the activities of the STG.

Who is involved?

The Solar Cooling STG is a group of AIRAH members who are passionate about innovation in the air conditioning industry and the potential that solar cooling brings as a renewable powered air conditioning technology.

Industry stakeholders are also registered with AIRAH to receive industry updates including the STG information stream which provides event-driven updates on developments in the solar cooling industry and activities of the Solar Cooling STG. Stakeholders come from a diverse background including:

Industry

Government

Academia

Public

The group is operated as a special technical group of AIRAH. STG membership enquiries or stakeholder information stream enquiries should be directed to STGS@airah.org.au.

Membership

What is Solar Cooling?

Solar Cooling is a technology which converts heat collected from the sun into useful cooling for delivery to applications such as building space conditioning. In this process, solar heat is collected and is used by a thermally-driven cooling process, which generates chilled water or conditioned air for use in the building. Chilled water is not widely used for cooling in residential applications but is used extensively in commercial buildings.

This process is summarised in the graphic below.

Solar cooling is a technology with a number of variants which exist due to the availability of a number of components which can be used in the solar heat collection, thermally-driven cooling process and delivery stages. The configuration of these components can also be altered. Broadly, however, solar cooling can be categorised into Open Cycle and Closed Cycle systems.

Solar cooling offers Australia an important opportunity to combat climate change by reducing the significant greenhouse gas (GHG) emissions generated by the electricity sector in servicing the residential and commercial building sectors. Solar cooling is uniquely suited to Australia because most of the population is located in subtropical or temperate regions which experience hot summers and relatively mild winters. Consequently, in Australia there is limited use for solar heat in buildings unless it can be used for space cooling.

Conveniently though, the maximum demand for space cooling typically coincides with the maximum availability of solar radiation (and therefore heat) for solar cooling, particularly in commercial buildings. This natural synergy between cooling demand and heat resource availability is ideal for solar cooling applications. Furthermore, some solar cooling technologies are capable of using diffuse radiation and have good storage capability - both of which can be of great significance on cloudy days.

The technical viability of this technology has been well established in a number of commercial-scale installations around the world, particularly in Europe. Despite this, solar cooling is a technology with many variants and no one approach has yet been found to be universally applicable. For these reasons there is a need to raise the profile of solar cooling in Australia, find solutions for Australian conditions and up-skill the local industry to rise to the challenge of developing and implementing effective solutions. The Solar Cooling STG has been established to achieve these goals.

How Solar Cooling works

Design

Solar Cooling systems are comprised of several key components/stages:

Firstly, the Sun's heat is obtained through the use of solar collectors, before being converted into cold using a “sorption” cooling process. The resulting cold must then be delivered to the application using a heat transfer medium which is typically chilled water or dry cool air. Thermal storage of the collected solar heat (or that of the produced cold) is often used to extend the operational hours of the solar cooling system. A number of alternative component technology options are available for each of these steps.

Component options for each stage include (note: not all listed options are compatible):

Each of the variants have advantages and disadvantages, and no one technology combination has yet been shown to be the optimum. For example, low cost collector technologies tend to only provide a low temperature source of heat which often requires a more costly or less efficient cooling process. Furthermore, application requirements or customer preferences may determine a delivery method which has a resultant impact on the selection of the cooling process and solar collectors.

Heat collection

Collector plant selection is dependent on the required operating temperature of the chosen cooling process.

Air collectors are relatively low-temperature collectors used to directly heat air. Air collectors are commercially available in Australia and have been particularly used for building space heating applications in cooler climates. Air collectors have substantial cost reduction potential through building fabric integration and appear most suited to air-based cooling processes such solar desiccant cooling.

Flat plate collectors have been used with single stage absorption chillers even though collector efficiency is reduced at the temperatures commonly used for driving the chiller. Flat plate collectors are widely available, low-cost collectors used extensively for heating water in the residential and light commercial sectors.

Evacuated tubes are used extensively in China and are increasingly appearing on the market in Australia. Evacuated tube collectors are non-tracking collectors capable of achieving significantly higher temperatures than that of flat plate collectors.

Tracking concentrating troughs reflect and focus direct-beam radiation onto a central receiver to achieve the highest temperatures and operate using oil, pressurised water or steam. The higher temperatures from trough collectors allow a more efficient two-stage absorption chiller to be used with a resulting reduction in the required area of the collector field.

With all collector technologies, designs should address the inevitable occurrence of much higher temperatures under stagnation conditions.

Cooling processes

Thermally-driven Cooling

Technologies used for converting solar heat into useful cooling include the following.

Desiccant cooling utilises liquid or solid desiccant material to dehumidify air. After dehumidification the air is sufficiently dry to enable an evaporative cooling process to cool air well below ambient temperature conditions. This air is then supplied directly to the building. This is an open cycle process where the cooling process utilises water as the refrigerant and air as the delivery media.

While there are relatively few suppliers of these systems, desiccant cooling systems have been used extensively in certain niche applications (e.g. supermarkets) where the ability to independently control air humidity provides additional benefits.

Adsorption chillers perform a closed cycle batch adsorption/ desorption process using a refrigerant and a solid adsorbent to achieve refrigeration. Refrigeration is used to cool down a secondary refrigerant circuit (chilled water or glycol) to enable the produced cold to be distributed to where it is required.

While there are only a limited number of Adsorption chiller manufacturers, adsorption chiller technology is able to operate with a lower temperature heat source and is more suitable for operation with a dry cooling tower.

Absorption Chillers use a liquid absorbent in a closed cycle process to achieve thermal compression of the refrigerant to create a refrigerating effect (although an absorption system does not compress vapour as such, it is a chemical process which has an affinity for the refrigerant vapour, absorbing it into solution, and in doing so it lowers the vapour pressure).

The resulting refrigeration process is used to cool down a secondary refrigerant circuit (chilled water or glycol) to enable the produced cold to be distributed to where it is required. Direct expansion systems are also available that do not require a secondary refrigerant.

Absorption cooling technology is mature, low cost and supplied by numerous manufacturers with most commonly available chillers requiring a wet cooling tower.

Absorption chillers are more efficient than other thermal cooling processes which means that less solar heat is required to achieve a given amount of cooling. Two-stage absorption chillers are even more efficient than single-stage units but require a higher temperature heat source. Even more efficient triple effect or three stage machines are also emerging onto the market.

Ejector refrigeration uses a thermal compressor (ejector) to compress a refrigerant without the use of any moving parts. The technology is robust but to-date the technology has not been widely used due to its relatively low efficiency.

Absorption and adsorption chillers are well suited to these applications and can operate in series with a conventional mechanical chiller, ideally with the absorption chiller providing lead cooling to maximise energy savings.

Where chilled ceilings are being used, the resulting elevated chilled water temperature enables lower temperature solar heat to be used. Similarly, heat rejection with a wet cooling tower is preferable to using a dry cooling circuit when attempting to use low temperature solar collectors.

In other buildings, package DX units are often used and chilled water is not included in the base design. In these buildings solar desiccant cooling configurations are likely to be more attractive.

In most cases, a backup form of cooling is required if comfort conditions in the occupied space are to be adequately controlled. This can be achieved through installation of;

A backup gas burner which provides heat (in place of solar heat) when required. In this case, no additional chiller/ cooling unit is required which makes this a low-capital cost option. However, unless the chiller is an efficient two-stage absorption chiller, the greenhouse gas (GHG) emissions from gas firing can reduce the savings that would otherwise be attributed to the solar cooling system

A backup (hot or cold) thermal storage tank to defer solar cooling until later in the day when solar heat is otherwise limited. While this can significantly increase solar fraction, it would be unusual to rely on this as the sole backup source.

Practical experience

Based on a recent European study, the (i) solar heat collection and (ii) cooling process steps account for around 50% of the cost of a solar cooling installation. Auxiliary equipment, control and other integration costs account for the remainder.

Typical energy savings from a solar cooling system are around 25% although savings promised at the preliminary design stages have sometimes been eroded by, inter alia, neglected parasitic energy consumption and insufficient attention to part load operation in the control scheme.

Given the maturity of the technology, expert assistance should be obtained to ensure that all the options have been considered and risks have been fully identified.

Is the equipment readily available in Australia?

Yes. Solar Cooling components are common industrial components with distribution agents available in Australia. However, when considering solar cooling you will also need to find skilled engineering expertise to integrate each of the components into a robust, economical and working system.

How much maintenance is required? Is it complex?

No, Solar Cooling maintenance is not complex. Lifetime efficiency will be maintained by cleaning collector glass and reflective surfaces at regular intervals.Absorption chillers require a schedule of maintenance for maintaining solution chemistry (corrosion inhibitors), vacuum and cooling tower infrastructure. However this is true in any HVAC system using Absorption chillers - not only Solar Cooling.

How much roof area is required?

This will depend on many factors including, inter alia, the level of backup chiller capacity. An indicative installation may require around 25% of roof area per unit of airconditioned floor space. Your design engineer can tailor to your specific constraints.

How much Greenhouse gas (GHG) can we save?

GHG savings will depend on the system, location and application. Though savings of around 25% are typical. Parasitic energy for fans, pumps etc should not be ignored. Depending on the system, excessive use of a gas burner, for backup heat, may also result in lower than expected greenhouse gas emission savings.

Why not just use conventional Air-conditioning with renewable power?

It is also possible to operate conventional vapour compression air conditioners using solar (PV) power. However, this method can be expensive and less efficient because there are several stages of energy conversion between sunlight and cool air.

What applications are most attractive for Solar Cooling?

A recent European study identified hospitals and hotels as particularly attractive targets. Shopping centres and recreational facilities are also expected to be attractive.

Australian Standard AS 5389:2013 published June 28, 2013

Australian Standard AS 5389:2013 Solar heating and cooling systems – Calculation of energy consumption was published on 28 June 2013. This standard is similar to AS/NZS 4234:2008 used for the calculation of energy savings and STCs for solar and heat pump water heaters, in that this standard is a method of calculating energy consumption using TRNSYS software. It allows energy savings to be calculated for solar systems that supply space heating and cooling, and domestic hot water systems using solar thermal collectors for thermal comfort. Furthermore, the AS 5389 standard can be used for system design and the optimisation of new systems.

At this stage, the standard outlines a performance test method for testing desiccant wheel-based air-conditioners, however it is intended that other space heating and cooling technologies will be included in the future.

AS 5389:2013 is an interim standard which is valid for two years. During this time comments about the standard will be accepted by the CS-028 committee, and the status of the standard will be reviewed.

The AIRAH Solar Cooling STG welcomes interested parties to comment on the standard regarding its usage and addition of other space heating and cooling technologies, as this standard is essential for the uptake of the technology into the industry and will allow the standard to cover a larger scope of technologies.

More information about the standard can be found on the Standards Australia website here.

AIRAH launches Solar Cooling Special Technical Group (09/05/2013)

AIRAH (the Australian Institute of Refrigeration, Air Conditioning and Heating) has launched its Solar Cooling Special Technical Group.

AIRAH’s special technical groups (STGs) provide a way of channelling specialist expertise from the wider industry into the Institute. They give their constituents – who are all AIRAH members as well as elite practitioners – a platform for involvement in issues that affect their discipline, including policy advice and regulation development.

AIRAH CEO Phil Wilkinson, M.AIRAH, says the aims of the AIRAH Solar Cooling STG are to advocate for solar cooling, to develop industry practitioner skills, to provide a hub for solar cooling information sharing, and to encourage better communication between stakeholders.

“As the sun beats down and air conditioners are turned up, what could be more logical than solar air conditioning? And with enthusiasm for solving Australia’s electricity grid issues, solar air conditioning could be one of the HVAC industry’s answers to reducing both greenhouse gas issues and electricity infrastructure costs,” Wilkinson says.

“So by developing skills and capacity in the use of solar cooling technology, the AIRAH Solar Cooling Special Technical Group will help enable the HVAC industry to access new business opportunities in the renewable energy industry.”

Dr Stephen White, M.AIRAH, from CSIRO Energy Technology, says the AIRAH Solar Cooling STG will address barriers to the development of a vibrant solar air conditioning industry across Australia. He says the STG has a number of tasks it will implement in order to achieve its goal of growing skills and capacity building.

These initiatives include developing a comprehensive web portal; holding a regular conference to share information and recognise project excellence; delivering quality solar cooling training; preparing an industry roadmap; submitting responses to government public consultation processes; contributing to solar cooling standard development; and supporting AIRAH’s Dennis Joseph Award for the innovative use of solar energy in HVAC&R.

“The AIRAH Solar Cooling Special Technical Group will develop a work plan to promote a level playing field for HVAC-based solutions in the renewable industry,” White says. “The STG will also disseminate the latest technical information on solar cooling – taking advantage of standards, guides and tools.”

White says Australia is one of the leading countries in the race to develop new solar air conditioning solutions.

“Solar cooling involves the transformation of solar energy into useful building air conditioning,” White says. “In terms of reducing emissions and lower energy costs, it makes a lot of sense.

“Now with the AIRAH Solar Cooling STG, the discipline will have some much needed structure, and the support of Australia’s most respected HVAC&R organisation, in order to help take solar cooling to the next level.”

ausSCIG Solar Cooling Crash Course (29/11/2011)

The Australian Solar Cooling Interest Group (ausSCIG) held another of its highly successful Solar Cooling Crash Courses at the Australian Technology Park on Tuesday November 29 as part of the AuSES Solar 2011 Conference Program. The course was led by Dr. Stephen White (CSIRO Solar Cooling Research Leader, ausSCIG Chair, IIR Australia Chair).

The course was designed as an overview of technical, economic and bigger picture aspects of solar cooling for newcomers to the industry. It also provided design tips and technical case studies for industry specialists.

ausSCIG Conference 2011 (16/03/2011)

ausSCIG’s 5th Conference was held in Canberra on March 16 at University House Hall, ANU, Canberra.

As we have grown to expect, the conference was well-attended with representatives from a cross-section of Australian industry including energy networks, equipment suppliers, renewable energy businesses, consultants and government. The key themes of the conference included the current status and state of the art for solar cooling technology, solar cooling for energy peak demand management, technology barriers and industry development.

Keynote speaker Daniel Mugnier (TECSOL, France), noted that Australia is at the forefront of world developments with a number of emerging equipment suppliers, a number of innovative commercial installations and a growing amount of local design expertise.